Epoxy removal process for microformed electroplated devices

ABSTRACT

The present invention is directed to a method of removing epoxy-based photoresist from a manufactured metallic microstructure or deep etched via, comprising the steps of (1) providing a form comprising an epoxy-based photoresist and a manufactured metallic microstructure; (2) optionally exposing the form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing the form to an alkali permanganate oxidizing solution to remove the form from the manufactured metallic microstructure, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the manufactured metallic microstructure to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 60/855,877 filed Nov. 1, 2006.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention is directed to the production of micromachines, microelectromechanical systems (MEMS) and more particularly to methods for producing high aspect-ratio plated microstructures and deep etched vias using an epoxy-based photoresist and removing the photoresist with a permanganate-based photoresist remover.

2. Brief Description of the Art

A wide variety of MEMS devices are now being fabricated using various types of UV sensitive photoresists. Epoxy-based photoresists, in particular are capable of producing very high aspect-ratio, micron-sized features with near perfect sidewalls. Some commercial applications of these photoresist structures can be found in ink-jet nozzles, micro-fluidic channels and bulk acoustic wave filters for wireless transmission. Other MEMS devices use these same epoxy-based photoresists as a microform or micro-mold to produce a secondary metallic image by electrolytic or electroless plating techniques. Once the metal micro-structure has been formed, the epoxy photoresist is removed, leaving behind the final plated metallic structure.

Removing the epoxy mold without harming the plated metal structure can be difficult, because many of the properties that make cured epoxy resins resistant to chemical attack from the plating solution also make them resistant to their removal in photoresist stripping chemistry. However, complete removal of the epoxy mold is critical for producing many MEMS devices, such as induction coils, harmonic micro-drives and fuel cell catalysts.

Advanced packaging and chip stacking techniques rely upon a method of perforating the completed wafer with microscopic holes, which pass completely through the substrate and are known as through-hole-wafer-vias. The vias are commonly formed using a dry, isotropic etching technique known as deep reactive ion etching (DRIE). The wafer vias are isotropic, because of a process (a.k.a. “Bosch”) of alternating gases of sulfur hexafluoride and octafluorocyclobutane. Alternating these two gases successively deposits and removes polymer in the etched vias, which acts to passivate the etched sidewall, which produces extremely high aspect ratio etched structures under vacuum and a radio frequency (RF) generated plasma. After the vias are completed, it is common to fill them with plated metals, such as copper or polycrystalline silicon.

Epoxy-based photoresists have been found to have very good resistance to fluorine and chlorine plasmas, making them an ideal photoresist for DRIE processing. However, removing the resist after several hours of exposure to high temperature DRIE conditions can be difficult or impossible.

Various methods for removing epoxy photoresists have been reported, such as the use of hot molten salts, excimer lasers, thermally stressing or cracking the resist, high pressure water jets and even sand blasting. However, to date no satisfactory method of removing or dissolving cross-linked epoxy resists from micron-sized metallic structures has been demonstrated. It is possible to modify the structure of the epoxy polymer and make it more susceptible to common photoresist removers, such as N-methyl pyrrolidine (NMP), as taught by U.S. Patent Application No. 2005/0147918 A1 and Japanese Patent No. JP 2007-109706. Such an epoxy resin, known as BMR, is commercially available from Nippon Kayaku Co. Ltd. Japan. It is also possible to remove the photoresist using dry processing techniques, such as reactive ion etching (RIE). However, RIE etch rates for photoresist stripping rarely exceed 1-2 μm per minute. This means that the dwell time for stripping photoresist from a single wafer can be almost two hours for a 100 μm coating of photoresist, whether the plasma is generated by RF or microwaves.

Because of the large number of wafers that can be simultaneously batch processed and because of its relatively low cost, wet chemical tank processing is the preferred method of photoresist removal. One such process that has been widely accepted in the preparation of printed circuit boards for through-hole metallization is a process called desmear or etchback. See, for example, U.S. Pat. Nos. 4,597,988; 4,515,829; 4,496,420; 4,601,783; 4,863,577; 5,498,311; 5,985,040; and 6,454,868. The printed circuit board, which consists of a matrix of glass fibers embedded in epoxy resin and interlaced with layers of copper metal, are commonly perforated using a high-speed drill. During the process of drilling the holes, the drill bit temperature exceeds the glass transition temperature (Tg) of the epoxy resin and spreads excess, unwanted epoxy into the drilled hole, making it difficult to plate the hole with electrolytic or electroless copper plating solutions. This thin layer of epoxy resin, which is “smeared” by the drill bit into the printed circuit board hole can be removed by treatment with a solution of alkali permanganate. This process, known as “desmear” removes the cross-linked epoxy resin by reacting it with an aqueous solution of alkali and permanganate to produce insoluble manganese dioxide and alkali soluble carboxylic acids (See Scheme. 1). The manganese dioxide precipitate is then removed by converting it to aqueous, soluble manganese sulfate in a subsequent neutralizer solution.

Improved methods of removing cross-linked epoxy resists for the production of MEMS and other micron-sized structures are needed in the art. The present invention is believed to be an answer to that need.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a method of removing epoxy-based photoresist from a manufactured metallic microstructure, comprising the steps of (1) providing a form comprising an epoxy-based photoresist and a manufactured metallic microstructure; (2) optionally exposing the form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing the form to an alkali permanganate oxidizing solution to remove the form from the manufactured metallic microstructure, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the manufactured metallic microstructure to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution.

In another aspect, the present invention is directed to a method of manufacturing a MEMS device, comprising the steps of: (1) providing a form comprising an epoxy-based photoresist and a manufactured MEMS device; (2) optionally exposing the form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing the form to an alkali permanganate oxidizing solution to remove the form from the manufactured MEMS device, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the manufactured MEMS device to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution.

In another aspect, the present invention is directed to a method of removing crosslinked epoxy novolak photoresist from a substrate, comprising the steps of: (1) providing a substrate comprising a form made from crosslinked epoxy novolak photoresist; (2) optionally exposing the substrate to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing the substrate to an alkali permanganate oxidizing solution to remove the crosslinked epoxy novolak photoresist from the substrate, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the substrate to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution.

In another aspect, the present invention is directed to a method of removing crosslinked epoxy-based photoresist, comprising the steps of: (1) lithographically producing an etch mask on a substrate with an epoxy-based photoresist; (2) exposing the substrate to a DRIE plasma comprising alternating gases of sulfur hexafluoride and octafluorocyclobutane; (3) exposing the substrate to an alkali permanganate oxidizing solution to remove the crosslinked epoxy novolak photoresist from the substrate, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the substrate to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution.

These and other aspects will become apparent upon reading the following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a method for producing high aspect-ratio, micron-sized structures in epoxy-based photoresists, plating and forming micron-sized metal structures between, under and/or around the micro-formed epoxy photoresist and removing said epoxy photoresist without deforming the plated metal structures. Such structures can be encountered in the fabrication of MEMS devices or in computer flip-chip packaging structures known as bumps.

There are several key differences which distinguish the use of an alkali permanganate process for producing MEMS devices from the preparation of printed circuit boards for plating. First, the desmear printed circuit board process is rate controlled, which means that time, temperature, pH and permanganate concentration all must be tightly controlled to prevent too much epoxy from being removed and exposing the many glass fibers that support the epoxy polymer. Second, the desmear process for printed circuit boards is performed prior to electrolytic or electroless plating.

The method of using alkali permanganate to remove epoxy-based photoresists for MEMS applications and for micro-machined parts is said to go to completion because all of the resist is removed from the metal plated structure. Therefore, the epoxy-based photoresist removal process stops when all of the resist is reacted and it is therefore not necessary for critical timing of the process step. In the event that the removal process is incomplete and that some epoxy-based photoresist still remains, the process steps can be repeated without adverse chemical reactions. Since the entire epoxy mold is removed in the alkali permanganate solution, a robust process can be obtained by incorporating a small excess process time and without analytical controls of the permanganate solution. Also, because the MEMS device plating is completed before the epoxy-based photoresist is removed, there are no issues with contaminating the plating solution with permanganate residue.

As indicated above, the present invention is directed to a method of removing epoxy-based photoresist from a manufactured metallic microstructure or deep etched via, comprising the steps of (1) providing a form comprising an epoxy-based photoresist and a manufactured metallic microstructure; (2) optionally exposing the form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing the form to an alkali permanganate oxidizing solution to remove the form from the manufactured metallic microstructure, the alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of the alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of the alkali permanganate solution; and (4) exposing the manufactured metallic microstructure to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of the neutralizing solution. Each of these steps is discussed in greater detail below.

According to the invention, a form made from an epoxy-based photoresist and a manufactured metallic microstructure may be any microstructure commonly employed in microelectronics manufacturing, such as a micromachined part, a microelectromechanical systems (MEMS) device, a metal plated part, computer flip-chip packaging structures, metallic bumps, and the like. Preferably, the metal microstructure has a high aspect ratio, and more preferably an aspect ratio of greater than two, where the aspect ratio is defined as the ratio of the height to width of the structure. The form may be made by any process or technique, such as lithography, electroplating, combinations of these techniques, and the like.

A preferred epoxy-based photoresist used in the method of the present invention is a carboxylated epoxy cresol novolak photoresist known as KMPR®, commercially available from MicroChem Corp. U.S.A. and also by Kayaku MicroChem Corporation of Japan. KMPR® photoresist is capable of producing near vertical, high aspect-ratio micron-sized structures, which can be used for either electrolytic or electroless plating.

The KMPR® photoresist plating form can be partially removed from the plated metallic structures by optionally pre-treating the form with a solvent, aqueous alkali, or amine based photoresist stripper solution. Examples of solvents or amine based strippers include N-methyl pyrrolidone (NMP), dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF), dimethylacetamide (DMAC), diethylene glycol monobutyl ether or propylene carbonate, as well as combinations of these. Examples of aqueous alkali include 20-45 wt % of aqueous sodium or potassium hydroxide. Preferably, this pre-treatment step occurs at a solution temperature of 60° C.-80° C.

Fully cross-linked KMPR® resist can be completely removed from the ultra-high aspect ratio, micron-sized metal-plated structures using an alkali permanganate oxidizing solution. The permanganate component of the alkali permanganate oxidizing solution is preferably selected from sodium or potassium permanganate. The concentration of permanganate in the alkali permanganate oxidizing solution is not critical, but is preferably in the range of from about 4% by weight to about 9% by weight, based on the total weight of the alkali permanganate solution. The alkali component of the alkali permanganate oxidizing solution is preferably selected from hydroxides such sodium hydroxide, potassium hydroxide, magnesium hydroxide, and the like. Other alkalis are known to those of skill in the art. The concentration of alkali in the alkali permanganate oxidizing solution is also not critical, but is preferably in the range of from about 3% by weight to about 6% by weight, based on the total weight of the alkali permanganate solution. One useful concentration is approximately 5% by weight of permanganate and 5% by weight of alkali, based on the total weight of the alkali permanganate oxidizing solution.

Conventional UV curable, epoxy-based photoresists, such as SU-8, commercially available from MicroChem Corp. U.S.A, are so highly cross-linked that hot N-methyl pyrrolidone (NMP) or other organic solvents cannot remove it from the wafer surface. Only strong acid-peroxide solutions are capable of removing SU-8 photoresist, but have the disadvantage of completely removing the metallic structures from the wafer as well. Therefore, the difficulty in removing cross-linked SU-8 can result in a wafer that, if improperly imaged, can be rendered unusable.

Alkali permanganate solutions have also been shown to be capable of removing thick coatings of cross-linked SU-8 photoresist from bare silicon wafers. This occurs even after prolonged hard baking of the patterned resist to temperatures as high as 150° C. The alkali permanganate process allows SU-8 patterned wafers to be reworked or reprocessed. Therefore, the fabrication cost of imaging with SU-8 photoresist can be reduced and the commercial viability increased by the use of this process.

Residual epoxy resist and manganese dioxide are removed from the metal structures by neutralizing (reducing) the manganese dioxide in a neutralizer solution that comprises (1) an acid, such as sulfuric acid, sulfamic acid, methane sulfonic acid, and the like, and (2) a mild reducing agent such as hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, and the like. The concentration of acid is not critical, but is preferably in the range of from about 5% by weight to about 10% by weight, based on the total weight of the neutralizer solution. The concentration of reducing agent is also not critical, but is preferably in the range of from about 1% by weight to about 10% by weight, based on the total weight of the neutralizer solution. The neutralizing solution process acts quickly and can be processed at 20° C.-25° C.

After the neutralizer step, the copper, nickel, gold, tin-lead or lead-free tin-bismuth-silver plated micro-structures remain intact, without distortion from any swelling or damage from the removal of the KMPR® photoresist.

EXAMPLES

The following examples are intended to illustrate, but in no way limit the scope of the present invention. All parts and percentages are by weight, and temperatures are in degrees Celsius unless explicitly stated otherwise.

Example 1

A copper MEMS structure was created by vacuum sputtering a 150 mm diameter silicon wafer with an adhesion layer of 200 Å titanium followed by 500 Å of a copper metal seed layer. A photoresist adhesion promoter containing hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000 rpm and then baked for 2 minutes at 95° C. A 50 μm coating of KMPR® 1050 epoxy-based photoresist (generically known as a carboxylated epoxy ortho cresol novolak photoresist and commercially available from MicroChem Corp., Newton, Mass.) was spin-coated for 30 seconds at 3000 rpm on the copper coated silicon wafer and baked for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture (commercially available from MicroChem Corp., Newton, Mass., as EBR PG) directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The coated wafer was then baked for 60 seconds at 65° C.

The coated wafer was then exposed using an EVG 620 aligner to 1100 mJ/cm² of 350-436 nm filtered UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide (commercially available from Rohm & Haas Electronic Materials Co., Marlborough, Mass. as CD-26), rinsed in deionized water and dried.

Once the imaged microform wafer was complete, it was cleaned using oxygen plasma in a reactive ion etcher (RIE, available from March Plasma Systems, Concord, Calif.). The wafers were plasma treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr. The patterned and cleaned wafer was then plated using a solution of copper sulfate and sulfuric acid (commercially available from Technic, Inc., Cranston, R.I., as Copper U Bath RTU), for 70 minutes at room temperature and a current density of 100 mA.

The patterned photoresist microform was removed from the plated copper structures and the copper seed layer by immersing the wafers in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of methane sulfonic acid for 2 minutes at room temperature.

Example 2

A nickel MEMS structure was created by vacuum sputtering a 150 mm diameter silicon wafer with a seed layer of 500 Å nickel metal. A photoresist adhesion promoter containing hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000 rpm and then baked for 2 minutes at 95° C. A 50 μm coating of KMPR® 1050 epoxy-based photoresist was then spin-coated for 30 seconds at 3000 rpm on the nickel coated silicon wafer and baked for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The coated wafer was then baked for 60 seconds at 65° C.

The coated wafer was then exposed using an EVG 620 aligner to 1100 mJ/cm² of 350-436 nm filtered UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed in deionized water and dried.

Once the imaged microform wafer was complete, the wafer was cleaned using oxygen plasma in a reactive ion etcher (RIE). The wafers were plasma treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr. The patterned and cleaned wafer was then plated using a solution of nickel sulfamate, for 70 minutes at room temperature and a current density of 100 mA.

The patterned photoresist microform was removed from the plated nickel structures and nickel seed layer by immersing the wafers in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of methane sulfonic acid for 2 minutes at room temperature.

Example 3

A metal solder bump structure was created by vacuum sputtering a 150 mm diameter silicon wafer with an adhesion layer of 200 Å titanium followed by another 500 Å of a copper metal seed layer. A photoresist adhesion promoter containing hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000 rpm and then baked for 2 minutes at 95° C. A 50 μm coating of KMPR® 1050 epoxy-based photoresist was then spin-coated for 30 seconds at 3000 rpm on the copper coated silicon wafer and baked for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The coated wafer was then baked for 60 seconds at 65° C.

The coated wafer was then exposed using an EVG 620 aligner to 1100 mJ/cm² of 350-436 nm filtered UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed in deionized water and dried.

Once the imaged microform wafer was complete, the wafer was cleaned using an oxygen plasma in a reactive ion etcher (RIE). The wafers were plasma treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr. The patterned and cleaned wafer was then plated using a solution of stannous sulfate, lead sulfate and sulfuric acid (commercially available from Technic, Inc. as Techni NuSolder JM-6000 LS), for 70 minutes at 45° C. and a current density of 100 mA.

The patterned photoresist microform was removed from the plated tin-lead structures and copper seed layer by immersing the wafers in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the KMPR® photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of methane sulfonic acid for 2 minutes at room temperature.

Example 4

Nickel air bridge and cantilever structures were created by vacuum sputtering a 150 mm diameter silicon wafer with a seed layer of 500 Å nickel metal and a zero layer alignment mark. A photoresist adhesion promoter containing hexamethyldisilazane (HMDS) was spin coated for 30 seconds at 3000 rpm and then baked for 2 minutes at 95° C. A 50 μm coating of KMPR® 1050 epoxy-based photoresist was then spin-coated for 30 seconds at 3000 rpm on the nickel coated silicon wafer and baked for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The coated wafer was then baked for 60 seconds at 65° C.

The KMPR® coated wafer was then exposed to 650 mJ/cm² of 350-436 mn filtered UV radiation with a photo-mask aligned to the zero layer using an EVG 620 aligner. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed in deionized water and dried.

The wafer was then cleaned using oxygen plasma in a reactive ion etcher (RIE). The wafers were plasma treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr. The patterned and cleaned wafer was then plated using a solution of nickel sulfamate for 70 minutes at room temperature and a current density of 100 mA. After plating, the wafer was rinsed in deionized water, dried and plasma treated for another 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr.

A second layer of KMPR® 1050 epoxy-based photoresist was coated directly on top of the patterned and plated first layer of KMPR® 1050 by spin coating for 30 seconds at 3000 rpm and baking for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The KMPR® coated wafer was then baked for 60 seconds at 65° C.

The KMPR® coated wafer was then exposed to 650 mJ/cm² of 350-436 nm UV radiation and aligned to the same zero layer with a different photo mask using an EVG 620 aligner. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed and dried.

The wafer was then cleaned again using oxygen plasma for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr and plated again using a solution of nickel sulfamate, for 70 minutes at room temperature and a current density of 100 mA. After plating, the wafer was rinsed in deionized water.

Once the imaged microform wafer was complete, the patterned photoresist microform was removed from the plated nickel structures and nickel seed layer by immersing the wafers in a solution of NMP for 20 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 20 minutes at 70° C. Finally, the manganese dioxide was neutralized and the photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at room temperature.

Example 5

A gold metal bump structure was created by vacuum sputtering a 150 mm diameter silicon wafer with an adhesion layer of 200 Å titanium followed by another 500 Å of a gold metal seed layer. A photoresist adhesion promoter containing hexamethyldisilizane (HMDS) was spin coated for 30 seconds at 3000 rpm and then baked for 2 minutes at 95° C. A 50 μm coating of KMPR® 1050 epoxy-based photoresist was then spin-coated for 30 seconds at 3000 rpm on the gold coated silicon wafer and baked for 15 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The KMPR® coated wafer was then baked for 60 seconds at 65° C.

The KMPR® coated wafer was then exposed using an EVG 620 aligner to 1100 mJ/cm² of 350-436 nm UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide (commercially available from Rohm & Haas Electronic Materials Co. as CD-26), rinsed in deionized water and dried.

Once the imaged KMPR® microform wafer was complete, the wafer was cleaned using an oxygen plasma in a reactive ion etcher. The wafers were plasma treated for 2 minutes with 100 W of DC power, 10 sccm of oxygen at a pressure of about 50 mTorr. The patterned and cleaned KMPR® wafer was then plated using a non-cyanide solution of auric sulfate (commercially available from Technic, Inc. as TechniGold 25 ES), for 70 minutes at 45° C. and a current density of 100 mA.

The patterned KMPR® photoresist microform was removed from the plated gold structures and gold seed layer by immersing the wafers in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the KMPR® photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at room temperature.

Example 6

A bare silicon wafer was stripped of cross-linked SU-8 photoresist (commercially available from MicroChem Corp.). A 50 um coating of SU-8 was first prepared by spin-coating SU-8 2050 for 30 seconds at 3000 rpm on an untreated silicon wafer and baked for 15 minutes at 95° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The SU-8 coated wafer was then baked for 60 seconds at 65° C.

The SU-8 coated wafer was then exposed using an EVG 620 aligner to 500 mJ/cm² of 350-436 nm filtered UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 95° C. and then developed in 1-methoxy-2-propanol acetate (commercially available from MicroChem Corp. as SU-8 developer), rinsed with isopropanol and dried. Once the patterned SU-8 wafer was complete, the wafer was hard baked for 30 minutes at 150° C.

The patterned SU-8 wafer was placed in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the SU-8 photoresist was completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at room temperature.

Example 7

The present invention may also be implemented in removal of highly crosslinked epoxy-based photoresist, such as KMPR® or SU-8 photoresist as described above, following exposure to fluorine plasma in a deep reactive ion etch (DRIE) processing. Briefly, one preferred embodiment of this aspect of the invention includes (1) lithographically producing an etch mask with an epoxy-based photoresist; (2) exposing the substrate to a DRIE plasma comprising alternating gases of sulfur hexafluoride and octafluorocyclobutane; (3) exposing the substrate to an alkaline oxidizing solution to remove the crosslinked SU-8 photoresist from the substrate; and (4) exposing the substrate to a reducing agent. The following example provides details of this embodiment.

A 1000 μm deep through-hole-wafer-via was created using a 10 μm coating of KMPR® 1010 epoxy-based photoresist (commercially available from MicroChem Corp.), which was spin-coated for 30 seconds at 3000 rpm on a bare silicon wafer and baked for 10 minutes at 100° C. The edge bead was removed using a fine stream of a dioxolane mixture directed at the edge of the wafer while spinning the wafer for 60 seconds at 600 rpm. The KMPR® coated wafer was then baked for 60 minutes at 65° C.

The KMPR® coated wafer was then exposed using an EVG 620 aligner to 500 mJ/cm² of 350-436 nm filtered UV radiation. After exposure, the wafer was post-exposure baked for 3 minutes at 100° C. and then developed in 0.26N tetramethyl ammonium hydroxide, rinsed in deionized water and dried. After drying, the wafer was hard baked for 30 minutes at 150° C.

After drying, the wafer was post-exposure baked for 3 minutes at 95° C. and then developed in 1-methoxy-2-propanol acetate, rinsed with isopropanol and dried. Once the patterned KMPR wafer was complete, the wafer was hard baked for 30 minutes at 150° C.

The KMPR® patterned and hard baked wafer was then etched in a Surface Technology Systems (manufactured by STS plc, Newport, UK) Multiplex ICP etcher for 8 hours using 600 W of coil power, 140 W of platen power, 140 sccm of sulfur hexafluoride and 95 sccm of octafluorocyclobutane at a pressure of 31 mTorr. This resulted in a 1000 μm deep silicon etch and which consumed only 16 μm of KMPR® photoresist.

The patterned KMPR® photoresist etch mask was removed from the through-hole-wafer-via by immersing the wafers in a solution of NMP for 10 minutes at 70° C. followed by immersing the wafers in a solution of 5% w/w sodium permanganate (NaMnO₄) and 5% w/w sodium hydroxide (NaOH) for 10 minutes at 70° C. Finally, the manganese dioxide was neutralized and the KMPR® photoresist completely removed by immersing the wafers in a solution of 5% w/w hydroxylamine sulfate and 2% w/w of sulfuric acid for 2 minutes at room temperature.

While the invention has been described above with reference to specific embodiments thereof, it is apparent that many changes, modifications, and variations can be made without departing from the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modifications, and variations that fall within the spirit and broad scope of the appended claims. All patent applications, patents, and other publications cited herein are incorporated by reference in their entireties. 

1. A method of removing epoxy-based photoresist from a manufactured metallic microstructure, comprising the steps of (1) providing a form comprising an epoxy-based photoresist and a manufactured metallic microstructure; (2) optionally exposing said form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing said form to an alkali permanganate oxidizing solution to remove said form from said manufactured metallic microstructure, said alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of said alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of said alkali permanganate solution; and (4) exposing said manufactured metallic microstructure to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of said neutralizing solution.
 2. The method of claim 1, wherein said epoxy-based photoresist is a crosslinked carboxylated epoxy cresol novolak photoresist.
 3. The method of claim 1, wherein said alkali permanganate oxidizing solution comprises about 5% permanganate by weight and about 5% alkali by weight, all based on the total weight of said alkali permanganate solution.
 4. The method of claim 1, wherein said reducing agent is selected from the group consisting of hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, and combinations thereof.
 5. The method of claim 1, wherein said acid is selected from the group consisting of sulfuric acid, sulfamic acid, methane sulfonic acid, and combinations thereof.
 6. The method of claim 1, wherein said solvent or amine-based photoresist stripper is selected from the group consisting of NMP, dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF), dimethylacetamide (DMAC), diethylene glycol monobutyl ether, propylene carbonate, and combinations thereof.
 7. The method of claim 1, wherein said manufactured metallic microstructure is a micromachined part.
 8. The method of claim 1, wherein said manufactured metallic microstructure is a metal bump.
 9. A method of manufacturing a MEMS device, comprising the steps of: (1) providing a form comprising an epoxy-based photoresist and a manufactured MEMS device; (2) optionally exposing said form to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing said form to an alkali permanganate oxidizing solution to remove said form from said manufactured MEMS device, said alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of said alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of said alkali permanganate solution; and (4) exposing said manufactured MEMS device to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of said neutralizing solution.
 10. The method of claim 9, wherein said epoxy-based photoresist is a crosslinked carboxylated epoxy cresol novolak photoresist.
 11. The method of claim 9, wherein said alkali permanganate oxidizing solution comprises about 5% permanganate by weight and about 5% alkali by weight, all based on the total weight of said alkali permanganate solution.
 12. The method of claim 9, wherein said reducing agent is selected from the group consisting of hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, and combinations thereof.
 13. The method of claim 9, wherein said acid is selected from the group consisting of sulfuric acid, sulfamic acid, methane sulfonic acid, and combinations thereof.
 14. The method of claim 9, wherein said solvent or amine-based photoresist stripper is selected from the group consisting of NMP, dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF), dimethylacetamide (DMAC), diethylene glycol monobutyl ether, propylene carbonate, and combinations thereof.
 15. A method of removing crosslinked epoxy novolak photoresist from a substrate, comprising the steps of: (1) providing a substrate comprising a form made from crosslinked epoxy novolak photoresist; (2) optionally exposing said substrate to a solvent, aqueous alkali, or amine-based photoresist stripper; (3) exposing said substrate to an alkali permanganate oxidizing solution to remove said crosslinked epoxy novolak photoresist from said substrate, said alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of said alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of said alkali permanganate solution; and (4) exposing said substrate to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of said neutralizing solution.
 16. The method of claim 15, wherein said alkali permanganate oxidizing solution comprises about 5% permanganate by weight and about 5% alkali by weight, all based on the total weight of said alkali permanganate solution.
 17. The method of claim 15, wherein said reducing agent is selected from the group consisting of hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, and combinations thereof.
 18. The method of claim 15, wherein said acid is selected from the group consisting of sulfuric acid, sulfamic acid, methane sulfonic acid, and combinations thereof.
 19. The method of claim 15, wherein said solvent or amine-based photoresist stripper is selected from the group consisting of NMP, dimethylsulfoxide (DMSO), sulfolane, dimethylforamide (DMF), dimethylacetamide (DMAC), diethylene glycol monobutyl ether, propylene carbonate, and combinations thereof.
 20. The method of claim 15, wherein said epoxy novolak photoresist is SU-8.
 21. A method of removing crosslinked epoxy-based photoresist, comprising the steps of: (1) lithographically producing an etch mask on a substrate with an epoxy-based photoresist; (2) exposing said substrate to a DRIE plasma comprising alternating gases of sulfur hexafluoride and octafluorocyclobutane; (3) exposing said substrate to an alkali permanganate oxidizing solution to remove said crosslinked epoxy novolak photoresist from said substrate, said alkali permanganate oxidizing solution comprising from about 4% to about 9% permanganate by weight, based on the total weight of said alkali permanganate solution, and from about 3% to about 6% alkali by weight, based on the total weight of said alkali permanganate solution; and (4) exposing said substrate to a neutralizing solution comprising from about 5% to about 10% by weight of an acid and from about 1% to about 10% by weight of a reducing agent, all weight percents being based on the total weight of said neutralizing solution.
 22. The method of claim 21, wherein said alkali permanganate oxidizing solution comprises about 5% permanganate by weight and about 5% alkali by weight, all based on the total weight of said alkali permanganate solution.
 23. The method of claim 21, wherein said reducing agent is selected from the group consisting of hydroxylamine sulfate, hydroxylamine nitrate, hydroxylamine phosphate, and combinations thereof.
 24. The method of claim 21, wherein said acid is selected from the group consisting of sulfuric acid, sulfamic acid, methane sulfonic acid, and combinations thereof. 